In recent years, according to finer structures and higher integration of semiconductor devices, it has become more important to manage particles. One of, the major problems in managing particles is dust caused by surface roughness produced at a peripheral portion (a bevel portion and an edge portion) of a substrate, such as a semiconductor wafer, in a manufacturing process of semiconductor devices.
FIGS. 1A and 1B are enlarged cross-sectional views showing examples of a peripheral portion of a wafer W. FIG. 1A shows, a peripheral portion of a straight-type wafer W having a cross-section formed by a plurality of straight lines. FIG. 1B shows a peripheral portion of a round-type wafer W having a cross-section formed by a curve. In FIG. 1A, a bevel portion B of the wafer W includes an upper inclined portion P and a lower inclined portion Q, which are inclined with respect to upper and lower surfaces of an outer circumferential portion of the wafer W, respectively, and a side surface R of the outer circumferential portion of the wafer W. In FIG. 1B, a bevel portion B of the wafer W includes a portion having a curvature in a cross-section of an outer circumferential portion of the wafer W. In FIGS. 1A and 1B, an edge portion of the wafer W includes an area E located between an inner boundary of the bevel portion B and an upper surface D of the wafer W, on which semiconductor devices are formed. In the following description, a peripheral portion of a wafer includes the aforementioned bevel portion B and edge portion E.
There has heretofore been known a polishing apparatus (peripheral portion polishing apparatus) for polishing a peripheral portion of a wafer. Such a polishing apparatus has been used for shaping an outer circumferential portion of a wafer prior to a formation process of semiconductor devices. Recently, such a polishing apparatus has been used for removing films as a pollution source attached to a peripheral portion of a wafer in a formation process of semiconductor devices or for removing surface roughness produced at a peripheral portion of a wafer, for example, for separating needle projections formed after formation of deep trenches in the wafer. When objects attached to a peripheral portion of a wafer are removed in advance, it is possible to prevent contamination of wafers, which would be caused by a transfer robot for holding and transferring wafers. Further, when surface roughness is removed in advance from a peripheral portion of a wafer, it is possible to prevent dust from being produced by separation of objects formed on the peripheral portion of the wafer.
There has practically been used a substrate processing apparatus having process units including a polishing apparatus (polishing unit) for polishing a peripheral portion of a wafer, a cleaning unit for cleaning the wafer, and a drying unit for drying the wafer. This substrate processing apparatus is employed to perform a sequence of processes on a wafer which include polishing a peripheral portion of the wafer. In this case, before a wafer that has been polished in the polishing unit is introduced into a subsequent process unit, it is necessary to examine whether objects such as a film attached to the peripheral portion of the wafer have been removed or whether roughed surfaces have been smoothened. For this purpose, an inspection unit to inspect a peripheral portion of a wafer has been developed. This inspection unit obtains an image of a peripheral portion of a polished wafer by using an imaging device such as a CCD camera and performs image processing on the image.
As described above, this inspection unit is used mainly for detecting defective portions in a peripheral portion of a wafer. The inspection results include the number and an area of the defective portions in the peripheral portion of the wafer. The conventional inspection unit cannot perform measurement of a shape of a wafer, such as a cross-sectional shape of the peripheral portion of the wafer or a radius of the wafer. Specifically, a shape of a wafer is not measured in the polishing unit, and a polishing state of the peripheral portion is not detected based on the measurement results of the wafer. Thus, operation management has not been performed in the polishing unit.
Further, the conventional inspection unit is expensive because it performs a high degree of image processing with use of an imaging device such as a CCD camera and an image processing device. Further, a long period of time is required for inspection because of image processing.
The conventional inspection unit is provided separately from the substrate processing apparatus including the polishing unit. Accordingly, in order to inspect a polished wafer, it is necessary to transfer a wafer polished in the polishing unit from the substrate processing apparatus into the inspection unit. Thus, the polishing process becomes complicated so as to lower the process efficiency. Further, if the inspection results show insufficiency of removal of defects or contaminants at the peripheral portion of the wafer in the polishing unit, it is necessary to return the wafer to the polishing unit and polish the peripheral portion of the wafer again. In such a case, the polishing process cannot be performed speedily.